The present disclosure pertains generally to firearms. In particular the present disclosure describes and explains the construction and use of a two-stage, drop-in trigger assembly, for M4/M16 (AR) firearms, which is compliant with what is described herein as the “European Standard”.
The “European Standard”, as used herein, requires that the safety selector must allow selection to the “SAFE” position when the hammer is in the upright or “as fired” condition. This upright condition of the hammer is also described herein as being an up/forward position. Once in this position it is desired that the bolt carrier be allowed to fully retract thereby cocking the hammer, without damaging any components of the trigger assembly. The European Standard requires a trigger assembly construction which is different from those constructions normally built for US produced M4/M16 (AR) firearms.
One prior art construction for a trigger assembly required the hammer to keep the trigger depressed when the hammer is in the upright position. This construction effectively prevents the safety selector from being turned to the “SAFE” position. This prior art construction is common for US produced M4/M16 (AR) platform rifles. Newer prior art trigger assembly constructions allow the safety to be set to “SAFE” with the hammer in the upright position. However, importantly these trigger assembly constructions are of the single stage, non-adjustable style.
In order to be compliant with the European Standard for a two-stage trigger assembly for the AR platform, the safety selector must be able to be placed into the “SAFE” position when the hammer is forward in the upright (fired) position. The present disclosure is directed to a novel and unobvious two-stage, drop-in trigger assembly which conforms to and is compliant with the European Standard. As used herein, the referenced drop-in style of trigger assembly is also described as a non-adjustable style of trigger assembly.
As further background for the present disclosure, the field of the present disclosure encompasses trigger assemblies for AR platform rifles. There are two basic classes of construction which include single-stage and two-stage. Each of these classes of construction is further divided into adjustable and non-adjustable subclasses.
A single-stage trigger assembly includes a sear notch which is below the hammer pivot axis. The radius to the release point of the hammer is typically approximately 0.30 inches (7.62 mm) from the hammer pivot axis. The hammer spring applies a torque to the hammer which develops a force at this radius which is relatively high. Accordingly, the single-stage trigger assembly is noted for having a long pull requiring considerable pressure on the trigger in order to fire the weapon. This trigger pull is usually notable for several starts and stops as the trigger pulls through this arc and this is commonly referred to as “creep”.
There is a subclass of single-stage trigger assemblies known as adjustable single-stage trigger assemblies which provides a method of reducing the amount of sear engagement by means of a block of some kind that can be adjusted by the user of the firearm (i.e. shooter) or a gunsmith. This provides a shorter trigger pull but typically without reducing the amount of trigger pressure required to fire the firearm. The hammer has a cam which keeps the trigger rotated when the hammer is in the upright or fired position. This effectively prohibits the rotation of the safety selector to the “SAFE” position.
A two-stage trigger assembly includes a construction where the sear surface on the hammer is relocated to an overhanging appendage which is typically at a radius of approximately 0.77 inches (1.96 cm) from the hammer pivot axis. Assuming use of the same hammer spring in the two-stage construction as used in the single-stage construction, there is a lower spring force which is developed. More specifically, the force developed at the sear surface is 0.3/0.77 or approximately 39% of the force of a typical single-stage trigger assembly.
A lower force at the sear surface reduces the amount or level of friction required to separate the hammer sear surface from the trigger sear surface thus requiring less trigger pressure to fire the weapon. The disconnector (also known as the rear hook) for a two-stage trigger assembly is given a second task. This rear hook is brought to bear against the backside of the hammer's overhanging appendage just prior to the hammer's release. This is felt as a second stage to the trigger pull which somewhat increases the amount of trigger pressure required to be applied to the trigger in order to release the hammer.
Because there is very little movement of the trigger required to accomplish this movement, the user of the firearm (i.e. the shooter) can simply pull the trigger to the second stage then hold it there until the shooter is ready to fire the weapon, thereby allowing for more accurate site position at the instant of firing. There is a subclass that is an adjustable two-stage trigger assembly wherein the shooter or his gunsmith can adjust a specific set of parts to have an even more precise amount of second-stage engagement.
It would be an improvement to the current state-of-the-art of two-stage, drop-in trigger assemblies if these constructions could be made compliant with the European Standard. This compliance requires that the construction enable the safety selector to be placed in the “SAFE” position when the hammer is forward in the upright (fired) position.